MDL-49368 qtypes match & multichice: cope with editing after attempt

Teachers should not radically edit a question after it has been
attempted. However, if they do, we should handle it gracefully, rather
than triggering PHP errors.

question/type/match/lang/en/qtype_match.php

@@ -26,6 +26,8 @@
 $string['availablechoices'] = 'Available choices';
 $string['blanksforxmorequestions'] = 'Blanks for {no} more questions';
 $string['correctansweris'] = 'The correct answer is: {$a}';
+$string['deletedchoice'] = '[Deleted choice]';
+$string['deletedsubquestion'] = 'This part of the question was deleted after the attempt was started.';
 $string['filloutthreeqsandtwoas'] = 'You must provide at least two questions and three answers. You can provide extra wrong answers by giving an answer with a blank question. Entries where both the question and the answer are blank will be ignored.';
 $string['nomatchinganswer'] = 'You must specify an answer matching the question \'{$a}\'.';
 $string['nomatchinganswerforq'] = 'You must specify an answer for this question.';

question/type/match/question.php

@@ -71,6 +71,25 @@ public function start_attempt(question_attempt_step $step, $variant) {
     public function apply_attempt_state(question_attempt_step $step) {
         $this->stemorder = explode(',', $step->get_qt_var('_stemorder'));
         $this->set_choiceorder(explode(',', $step->get_qt_var('_choiceorder')));
+
+        // Add any missing subquestions. Sometimes people edit questions after they
+        // have been attempted which breaks things.
+        foreach ($this->stemorder as $stemid) {
+            if (!isset($this->stems[$stemid])) {
+                $this->stems[$stemid] = html_writer::span(
+                        get_string('deletedsubquestion', 'qtype_match'), 'notifyproblem');
+                $this->stemformat[$stemid] = FORMAT_HTML;
+                $this->right[$stemid] = 0;
+            }
+        }
+
+        // Add any missing choices. Sometimes people edit questions after they
+        // have been attempted which breaks things.
+        foreach ($this->choiceorder as $choiceid) {
+            if (!isset($this->choices[$choiceid])) {
+                $this->choices[$choiceid] = get_string('deletedchoice', 'qtype_match');
+            }
+        }
     }
 
     /**
@@ -80,8 +99,8 @@ public function apply_attempt_state(question_attempt_step $step) {
      */
     protected function set_choiceorder($choiceorder) {
         $this->choiceorder = array();
-        foreach ($choiceorder as $key => $value) {
-            $this->choiceorder[$key + 1] = $value;
+        foreach ($choiceorder as $key => $choiceid) {
+            $this->choiceorder[$key + 1] = $choiceid;
         }
     }
 

question/type/match/renderer.php

@@ -137,6 +137,9 @@ public function correct_response(question_attempt $qa) {
         $choices = $this->format_choices($question);
         $right = array();
         foreach ($stemorder as $key => $stemid) {
+            if (!isset($choices[$question->get_right_choice_for($stemid)])) {
+                continue;
+            }
             $right[] = $question->make_html_inline($this->format_stem_text($qa, $stemid)) . ' – ' .
                     $choices[$question->get_right_choice_for($stemid)];
         }

question/type/multichoice/lang/en/qtype_multichoice.php

@@ -38,6 +38,7 @@
 $string['clozeaid'] = 'Enter missing word';
 $string['correctansweris'] = 'The correct answer is: {$a}';
 $string['correctfeedback'] = 'For any correct response';
+$string['deletedchoice'] = 'This choice was deleted after the attempt was started.';
 $string['errgradesetanswerblank'] = 'Grade set, but the Answer is blank';
 $string['errfractionsaddwrong'] = 'The positive grades you have chosen do not add up to 100%<br />Instead, they add up to {$a}%';
 $string['errfractionsnomax'] = 'One of the choices should be 100%, so that it is<br />possible to get a full grade for this question.';

question/type/multichoice/question.php

@@ -64,6 +64,24 @@ public function start_attempt(question_attempt_step $step, $variant) {
 
     public function apply_attempt_state(question_attempt_step $step) {
         $this->order = explode(',', $step->get_qt_var('_order'));
+
+        // Add any missing answers. Sometimes people edit questions after they
+        // have been attempted which breaks things.
+        foreach ($this->order as $ansid) {
+            if (isset($this->answers[$ansid])) {
+                continue;
+            }
+            $a = new stdClass();
+            $a->id = 0;
+            $a->answer = html_writer::span(get_string('deletedchoice', 'qtype_multichoice'),
+                    'notifyproblem');
+            $a->answerformat = FORMAT_HTML;
+            $a->fraction = 0;
+            $a->feedback = '';
+            $a->feedbackformat = FORMAT_HTML;
+            $this->answers[$ansid] = $this->qtype->make_answer($a);
+            $this->answers[$ansid]->answerformat = FORMAT_HTML;
+        }
     }
 
     public function get_question_summary() {

question/type/multichoice/questiontype.php

@@ -174,6 +174,11 @@ protected function initialise_question_instance(question_definition $question, $
         $this->initialise_question_answers($question, $questiondata, false);
     }
 
+    public function make_answer($answer) {
+        // Overridden just so we can make it public for use by question.php.
+        return parent::make_answer($answer);
+    }
+
     public function delete_question($questionid, $contextid) {
         global $DB;
         $DB->delete_records('qtype_multichoice_options', array('questionid' => $questionid));